Right now, it appears there are some bugs occurring, and it's swaying the results of these 2 pets into a far different set than what we were seeing and testing on beta at level 80.
To start, on the beta, the imp's in combat (while casting) regen rate was around 40 mp5. It's OOC was 400 mp5.
Currently on live, the in combat regen rate appears to be around 100 mp5 (maybe a tad more). It's OOC is still 400 mp5.
What this means, is that on the beta the imp would go OOM about 3-4 minutes into a fight in a raid situation. Currently on live it can go that long without ANY raid mana regeneration, solely sustaining itself that long on its own mana pool and regen rate.
I presume this is a bug, but I guess time will tell.
The felhunter. On the beta, the felhunter would get upwards of 350+ dps for an affliction warlock. The imp would only get around 240 on your average fight. Currently this is not the case.
Currently the felhunter seems to be bugging, and stops casting shadowbite at times. At other times he actually stops attacking altogether. I'm still collecting data, but I have several WWS reports of my own where on boss fights he's got an exorbitant amount of downtime (ie, not attacking), even though he should have been attacking the entire time.